Reference is hereby made to the Microfiche Appendix "A" forming a portion of this specification and containing 1 microfiche and a total of 34 frames.
This invention is directed to a multiple load control apparatus for a multiple inputted load apparatus and particularly to a step-type controller for a water heater or like load means having a plurality of selectively actuated heating elements. .
Multiple input apparatus may include a plurality of individual actuated load inputs for controlling the state of or conditioning the load apparatus by sequential and selective actuation of such plurality of inputs. For example, water heating apparatus may be constructed with a plurality of individual heating elements or units rather than one single modulated element for varying the thermal energy inputted into the stored water. The heat input may be conveniently controlled by varying of the number of the heating elements which are activated at any given time. The actuation of the heating elements may be varied depending upon the temperature of the stored water, the time of day, the anticipated usage, the recovery rate requirements and any other factor or condition which can effect the heat input requirement. In such a system, it may be desirable to provide for particular types of sequential operations of the load devices. This in turn requires proper sensing and monitoring of status of all such load input devices as well as the various control factors, and then controlling the load or element activations in accordance with the predetermined relative sensed and monitored conditions.
Various means have also been suggested for controlling the turn-on and off of the several heating elements. For example, U.S. Pat. No. 3,787,729 discloses a water heater control system in which the heating elements are turned on and off with a first-on, first-off energizing sequence, and canousely, a last-on, last-off de-energizing sequence. This tends to prevent continued usage of a single heating element. The system suggested therein, thus provides a register-type record of the sequence of turn-on and turn-off so an appropriate element can be selected.
A particularly satisfactory step-type controller for such a system having a plurality of individual load means which are individually and separately activated with a first-on, first-off, and a last-on, last-off sequence and further based on operating factors is shown in the inventor's U.S. Pat. No. 4,333,002 which permits appropriate modification as well as recording of the first-on and last-on heating elements. As shown therein, as applied to a water heater unit having a plurality of individual electrical heating elements, the total number of heating elements on at any time is related to the difference between the actual water temperature and a preset desired water temperature with a differential span or dead band to prevent hunting in the control system. A microprocessor unit is coupled correspondingly and periodically sense the conditions of the sensors and signal sources as well as monitoring and storing the on-off status of each of the heating elements. The historical sequence of when each heating element was last turned on or off in relationship to all of the other heating elements is particularly monitored. The microprocessor periodically updates the status by processing of the last read and stored signals to develop the difference between the actual and desired water temperatures, dividing the same by the span setting signal to provide for a predetermined acceptable variation and adding a constant to produce a number corresponding to the number of elements which should be in an activated state for that condition. Such number is compared with the actual number of elements then on, and if there are any deviations, appropriate control signals are generated to increase or decrease the number of activated elements to the predetermied and preset number for that temperature condition.
The logic unit can readily store the historical sequence and when required, turn off the load from all loads then on which was the first to be turned on and to turn on the load from all loads then off which was first to be turned off. This then provides a sequence wherein the first-on is the first-off, and the last-on is last-off in the turn-on and turn-off sequences of operation. Other multiple load control systems are shown in the citation in the above patents.
In this manner a more or less generalized equalization of the loading of the elements is created. Although providing improved control over various other forms of logical systems, the individual elements may be operated with abnormal and undesirable extended periods.
There is therefore a need for an improved system for equalizing the load operations and thereby providing increased efficiency and overall system life operation.